It is known to use various paving slabs when constructing walkways over decks, podiums, terraces, pool decks, and roof promenades. Generally, precast concrete blocks are used and the conventional method is to set the blocks directly into sand, gravel, mortar beds, or onto the insulation or membranes positioned over a roof structure. This practice has been unacceptable because weather conditions can cause the blocks to dislocate or shift, thereby causing voids or even cracks in these structures. Additionally, water generally seeps below the blocks or slabs, and causes erosion of the sand or gravel support and the resulting shifting of the blocks. Water that enters below the block surface not only deteriorates the support layer, but also because of the freeze-thaw cycle, eventually damages the membranes and destroys their waterproofing capabilities. As a result of this support deterioration, many surfaces have to be uprooted and resurfaced or at least the blocks re-aligned. Repairs are frequent and costly, and replacing of membranes occurs often.
To correct this problem, various blocks or paver support systems similar to those disclosed in U.S. Pat. Nos. 3,861,098 and 3,892,902 have been introduced into the construction industry. Many of these new structures and, in particular, the pedestal defined in U.S. Pat. No. Des. 259,283 have been successful in reducing substantially the damage caused by the entry of surface water into these structures. Because the pedestal of this above-noted patent has an elevated support portion, walk deck surfaces can be elevated to provide a drain conduit between the blocks or pavers and the support surface covered by a waterproofing membrane. This pedestal comprises a gridlike structure of a high density polymeric material such as polyethylene having integral spacer ribs positioned on the upper surface of the pedestal. These spacer ribs guide and maintain in position the corner portions of a block or paving slab and provide spacing and cushioning between each block. The lower portion of the block then rests over the upper face or grid of the pedestal, permits any moisture to fall below the block and drain away without damaging the block or support surface. The pedestal, because it incorporates a unique through drainage and air-vent design, eliminates water entrapment and consequent damage to the corners of the paver slab or blocks.
Even as effective as the pedestal of U.S. Pat. No. Des. 259,283 has been, there are some structural improvements that need attention. This is especially apparent when these pedestals are stacked and some degree of lateral movement occurs. This lateral shifting or movement is very undesirable because when the units are multiple stacked in halves or quarter modules there is no interlocking of them to keep them together. Also they cannot property support loads and if shifting occurs, collapse of the structure results. In addition, because of the thickness of the material in the formed spacer rib, a substantial amount of shrinkage and distortion after molding could occur. This causes resulting pedestals of non-uniform configuration which is fatal when alignment and stacking are features necessary for proper usage. A further drawback in this pedestal configuration is the flashing or surface extension that is a result of the mold pressure needed to get proper cavity fill during the manufacturing operation. The flashing caused could seriously impede the water drainage feature of the pedestal.
Therefore, successful as this particular pedestal has been, it nonetheless can be substantially improved by structural improvements and modifications.